May 27, 2022 at 12:43 pmWhite_LeeSubscriber老师您好，请问为什么石墨烯的化学势无法设置为负数？当仿真双层石墨烯结构时，两层石墨烯分别加电压大小相同、正负相反的电压，这时两层石墨烯的化学势（即费米能级）应该分别是一正一负、数值相同的。
May 27, 2022 at 5:41 pmGuilin SunAnsys Employee我估计这个是一个选择参考零点的问题。相反电压只是向两个方向改变势能，实际的势能可能并不是负的，是相对参考点才成为负数的。
Fermi level referencing and the location of zero Fermi level
Much like the choice of origin in a coordinate system, the zero point of energy can be defined arbitrarily. Observable phenomena only depend on energy differences. When comparing distinct bodies, however, it is important that they all be consistent in their choice of the location of zero energy, or else nonsensical results will be obtained. It can therefore be helpful to explicitly name a common point to ensure that different components are in agreement. On the other hand, if a reference point is inherently ambiguous (such as "the vacuum", see below) it will instead cause more problems.
A practical and well-justified choice of common point is a bulky, physical conductor, such as the electrical ground or earth. Such a conductor can be considered to be in a good thermodynamic equilibrium and so its µ is well defined. It provides a reservoir of charge, so that large numbers of electrons may be added or removed without incurring charging effects. It also has the advantage of being accessible, so that the Fermi level of any other object can be measured simply with a voltmeter. https://en.wikipedia.org/wiki/Fermi_level
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